The present embodiments relate generally to communication networks, and more particularly, to a distributed fairness algorithm for dynamic bandwidth allocation on a ring.
An example of a communications network is a synchronous optical network (SONET). In particular, SONET is a transmission system technology for use on fiber optic cable networks. SONET systems carry traffic called the payload with overhead blocks. The overhead blocks include section, line, and path overheads. The section and line overheads together are identified as the transport overhead. The path overhead is an end-to-end overhead, while the line and section overheads help move data from one SONET component to another.
SONET specifies a digital hierarchy based upon optical carriers (OCs). SONET defines Synchronous Transport Signals (STSs) which are electrical interfaces used as the multiplexing mechanisms within SONET. SONET network elements (NEs) multiplex STS-1s into STS-N where needed. N is the number of STS-1s that form the STS-N.
High bandwidth connections are accommodated by concatenating STS-1s up to the aggregate speed required. In general, the concatenated STS-1s are designated with a xe2x80x9cc.xe2x80x9d For example, STS-3c represents three STS-1s and provides on the order of 155 Mbps for video and other high speed applications. SONET is multiplexed at the byte level permitting dynamic mapping of services into the broadband STS for transport.
SONET uses optical circuits that operate at prescribed speeds. For example, an STS-1 (or OC-1) operates at a bit rate of 51.840 Mbps and provides a capacity of 28 DS-1 (digital signal level 1) channels or 1 DS-3 (digital signal level 3) channel. An STS-3 (or OC-3) operates at a bit rate of 155.520 Mbps and provides a capacity of 84 DS-1 channels or 3 DS-3 channels, and so on as is known in the art. In addition, SONET bit streams are divided into frames. The frames are 810 characters in size with 36 characters of overhead and 774 characters of payload. On a SONET link, there are 8,000 (125 xcexcsec long) frames per second with 810 characters per frame and 8 bits in a character, resulting in a basic SONET transmission speed of 51.84 Mbps. As per above, the transmission speed of 51.84 Mbps is the SONET OC-1 basic channel.
With respect to ring architectures, the SONET building block for a ring architecture is the ADM. ADM represents an add/drop multiplexer. The ADM is a multiplexer capable of extracting and inserting lower-rate signals from a higher-rate multiplexed signal without completely demultiplexing the signal. ADMs can be put into a ring configuration for either bi-directional or uni-directional traffic. A main advantage of the ring topology is its survivability; that is, if a fiber cable is cut, the multiplexers have the intelligence to send the services affected via an alternate path through the ring without interruption.
However, there exist certain limitations in connection with the ring architecture. For example, conventional bandwidth allocation is known in the circuit switched domain with respect to the interconnection of packet switches and routers on a ring. Such allocations are typically performed at a transport node in an appropriate unit, such as an STS-1. The issues related to such conventional bandwidth allocation include:
1) The granularity of bandwidth allocation is inconsistent with the actual requirements. This results in an inefficient usage (i.e., a wastage) of valuable network resources.
2) The bandwidth allocation assignment is normally pre-configured and is difficult to update dynamically. Such pre-configured bandwidth allocation assignment is inconsistent with the bursty nature of the connected nodes.
One protocol known in the art includes a Dynamic Packet Transport (DPT) protocol, such as commercially available from Cisco Systems, Inc. of San Jose, Calif. While it addresses some of the above mentioned limitations, the DPT protocol suffers from configuration issues when the bandwidth demands are highly asymmetric.
Therefore, what is needed is an improved method and apparatus for providing more efficient usage of network resources in conjunction with bandwidth allocation on a ring.
According to one embodiment, a method for dynamic bandwidth allocation in a packet switched network having a ring architecture includes monitoring an occurrence of a contention of resources at a participating node and its neighboring nodes on the network. In response to a monitored occurrence of the contention of resources, bandwidth is dynamically allocated according to a fairness algorithm. Dynamically allocating bandwidth resolves contention of resources in a fair manner within given fairness constraints while enabling a prescribed maximum utilization of available bandwidth between the nodes. Lastly, the fairness algorithm generates fairness criteria in response to states that are local to the participating node and states obtained from the neighboring nodes.
A technical advantage of this embodiment is that a more efficient usage of network resources in conjunction with bandwidth allocation on a ring is made possible.